I think a more basic way of describing it is that he was one of the last scientists to hold onto the theory of needing an "aether" for EM waves to travel through.

The Michelson Morley experiment was in the 1880s and Tesla held on to the "luminiferous aether" theory until he died in the 1940's I believe. I seem to remember that he thought all other theories were "flawed" like you said.

People will say "Tesla was smart but not a good businessman, etc" and obviously he was a smart guy but still a tragic figure for holding onto old theories some of which bankrupted him.